Method for making high voltage high altitude bushing



Dec. 29, 1964 Original Filed May 2, 1955 W. A. SMITH ETAL METHOD FOR MAKING HIGH VOLTAGE HIGH ALTITUDE BUSHING Expose WIRE STRIP lusuLA'nou Arrzx RECEPTACLE APPLY PLAST\C\ZER T9 LoosE U lusuunau N va INSULATION EvAPonAT:

PLAen-amzsk 2 Sheets-Sheet l To Coysn SHRINK RECEPTACLE lusuuu'lou INVENTOR. WILLARD A- I'MTH EAm. M. KLEMER I W v Dec. 29, 1964 w. A. SMITH ETAL METHOD FOR MAKING HIGH VOLTAGE HIGH ALTITUDE BUSHING Original Filed May 2, 1955 2 Sheets-Sheet 2 mu mm E5 u WA v R A. M wEM w United States Patent 0 itillard Pm, as

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This invention relates in general to electrical connections, and in particular to high altitude high voltage bushings for providing a fluid tight lead-in to sealed electrical units, such as are employed in high altitude aircraft, guided missiles and the like.

The deterioration of the insulation qualities of air caused by the drop in atmospheric pressure on reaching the higher altitudes now attainable has rendered inadequate high voltage lead-in connectors as have been heretofore employed. For example, studs brought out through ceramic insulators are subject to arcing from stud to stud or from stud to the metal casing where reliance is placed in whole or in part on the diel ctric strength of air. Also commonly employed as high voltage connectors are plug-type arrangements where the connection is provided with a surrounding insulating sleeve, the assembly being enclosed in a supporting metal jacket. The free path from connection to jacket within such connectors is subject to arcing at high altitudes, and furthermore, the seal against oil seepage for hermetically sealed oilfilled units has in general been found to be unsatisfactory.

It is, therefore, an object of the present invention to provide an improved bushing assembly suitable for use with high voltages at altitudes.

Another object is to provide a lead-in bushing assembly for hermetically sealed electrical units wherein reliance on an air-gap as a dielectric material is avoided.

Another object is to provide a lead-in bushing which is of high quality and effectiveness yet simple in construction and inexpensive to produce.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described several embodiments; it is to be understood, however, that these embodiments are not intended to be exhaustive or limiting of the invention but are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

in the drawings:

FIGURE 1 is a schematic block diagram showing the proc ss steps of the inver on;

lelGUliES 25 are schematic views of the different steps of the process of the invention positioned relative to the step-blocks shown 1.

FIGURE 6 is a partial sectional view of a lead-in bushing according to the present invention; and

7 is a partial sectional view of another 6H1- bodiment of the invention.

Qorresponding parts in the figures are indicated by r reference characters. in following the description of the process or the inv there a correlation bean sen the step-blocks of F are l and the individual 2-5. With ref nce to the first step of the invention, for example, a comparison r made between the first level of blocks and PE U E 2, the second bloclr level and FliiUlE 3, etc. This, with the detailed description of PlGURES 6 7, should mall the invention adequately clear.

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With reference to FIGURE 6, numeral 1 designates the casing of a sealed electrical unit through which the bus-i .ng of the invention provides for the coupling of an external lead with the lead 5 connected to the electrical components of the unit, not shown. The bushing includes a cylindrical hollow body portion 7 of a suitable dielectric material, preferably ot a type which can be threaded, molded in plastic, and subjected to the wide range of temperatures encountered in high altitude applications and bonding operations, soldering, without cracking, such as a laminated phenolic-base resin, steatite ceramic and the line. The dielectric material selected will, however, depend to some extent on the method employed to seal the electrical unit. For example, if the unit is encased in a metal can for hermetic sealing, steatite ceramic metalized to provide a surface 9 extending circumieren'tially of portion 7 which is solderable to casing thereby to achieve a fluid-ticht seal preventing seepage of oil around the bushing. Alternatively, a laminated phenolic suffices where the electrical unit is embedded, or potted, in plastic.

To ellcct the electrical coupling of leads 3 and 5 within body portion '7, there is provided a separable contact assembly, preferably of the receptacle and mating pin type, which includes plug 11 having at one end a contact pin 13 and at the other end a solder well 15 in which lead 5 is soldered. Plug ill is ri idly maintained, as by solderor b fg, in the aperture 17 of a disc-like contact retainer l9 which snugly fits within the internally enlarged end 23 of body portion To perfect the scaling of the bushing, relative to inside of easing 1, end 21 is metalized in a conventional manner whereby contact retainer may be soldered in place thus rigidly disposing pin 13 in mating, position cozudally in tne bushing.

The receptacle portion 23 of the contact assembly includes at one end a socket 225 havin a cylindrical bore for receiving pin 13 and at other end a solder Well 27 which the wire core of external lead 3 is soldered. Serving to secure lead 3 within and to seal the outer end of the bushing is a fitting which includes a resilient 0 ring 31 of a size to fit tightly about the insulation of lead 3, and a cap 33, of a dielectric material similar to body portion '7, cap having a central aperture 35 Us through which lead 3 may be inserted and being internally threaded for cooperation with external threads cut on end of. body portion 7.

Ring is sl. ed back along the insulation of lead 3 until it will abut end face 37 of body portion '7 as pin 13 becomes fully seated in socket Tightening cap 33 on threaded end 29 serves to compress and flatten 31 'inst face 3'3, the consequent radial extrusion of ring ate the insulation of lead 3 effecting a fluid-tight seal -tside end of body portion To assure maximum protection against arcing it is preferred that body poi n '7 be filled as completely as possible with solid dielectric encompassing the metallic elements of the contact assembly, and with any remaining air space being replaced by any suitable viscous dielectric material chemical'y non-reactive with dielectrics forming the stucture. To this end, the inside diameter of body portion 2 is only sufiiciently lar er than the insulation diameter of lea 3 to admit lead without difficulty so that with an insulating jacket covering receptacle 23 to the mouth socket 25, substantially all the space within the bushing will be occupied with dielectric material. Prefera ly the insulation jaclrcting receptacle cornprises are unbchen insulation covering of lead 3, which insulation is slipped over the receptacle by any suitable method according the type of materials employed. By way of example, typical insulating materials utilized for high voltage leads are silicone-rubber or natural rubber compositions which expand upon soaking in temporary liquid plasticisers, such as the aromatic liquids toluene, benzene, or their derivatives. Accordingly, after stripping the end of lead 3 of insulation to expose the wire core for soldering in well 27, expanding the remaining insulation, as by soaking a silicone-rubber composition in toluene, permits the insulation to be easily pulled along the wire core and over receptacle 23. Upon evaporation of the toluene, the insulation composition shrinks to its original diameter into tight engagement with the wire core and contact receptacle as shown. Alternatively, for short lead lengths the insulation may simply be forced mechanically along the wire after soldering receptacle 23 to the wire core. Where a silicone-rubber composition is employed as the insulation for lead 3, a silicone grease is suitable for filling any voids remaining upon assembly of the bushing.

With reference to FIGURE 7, for lead insulation materials which are not conveniently movable relative to the associated wire core, an insulating jacket for receptacle 23 may be built up with sleeves 39 and 41 of suitable plastic material maintained in place by a force-fit engagement with the parts. For example, sleeves 39 and 41 may be vinyl-base plastics shrunk into place after expansion by soaking in a suitable plasticiser as is conventional in the art, sleeve 39 providing the main insulation jacket surrounding receptacle 23 and part of lead 3 and sleeve 41 serving as a filler to increase the etfective diameter of receptacle 23 to substantially the lead insulation diameter.

In the alternative embodiment shown in FIGURE 7, where increased dielectric strength and resistance to charring is desired, body portion '7 may be formed of glass. To provide surfaces on which bondin operations, such as soldering, may be performed, circumferential bands 43, 45 and 47 of the glass body are fired with silver by con ventional techniques, bands 43, 45 and 47 respectively providing surfaces for bonding the bushing to casing l, threaded metallic ferrule 4'9 to the outer end of body portion 7, and contact retainer 51 to the inside end of body portion 7. Contact retainer 51 supports plug 11 and the threads on ferrule 49 serve as the means by which cap 33 is attached to the bushing.

Sleeve 39 extends sufficiently far back along the lead to provide a stop for cap 33 which during assembly of the bushing abuts the end of sleeve 39 before the threads on ferrule 49 are exhausted. Further tightening of cap 33 jams sleeve 39 into forceful engagement with body portion 7 thereby effecting a fluid-tight seal at the cap end of the bushing. The bonding at bands 43, 45 and 47 render the bushing completely sealed against penetration of any foreign matter.

We claim:

1. The method of insulating a contact assembly having mating elements including the steps of exposing the end of 4 the wire core of an insulated lead, affixing the wire end to the contact element having exposed surfaces upon joining the contact assembly in mating relationship, loosening the insulation of the lead relative to the wire core, and moving the insulation along the'wire core to cover substantially the exposed surfaces of the contact element and wire core with insulation continuous with the insulation of the lead.

2. in the forming of an insulated contact assembly including mating contact elements, the method of insulating the contact element having the exposed surfaces upon joining the elements in mating relationship including the steps of exposing the end of the wire core of a lead insulated with a plastic material, aiiixing the wire end to the contact element, soaking the insulation of the lead in a temporary plasticiser to expand and loosen the insulation relative to the wire core, moving the expanded insulation along the wire core to cover substantially the exposed surfaces of the contact element and wire core with insulation continuous with the insulation of the lead, and evaporating the plasticiser to shrink the insulation into tight engagement with the contact element and wire core.

3. The method of insulating a contact assembly having elongated mating contact elements including the steps of stripping oif the end segment of insulation of an insulated lead wire to expose the wire core, affixing the exposed wire core to the contact element having exposed surfaces upon joining the contact assembly in mating relation, loosening the remainder of the insulation of the lead wire relative to the wire core, and moving the loosened insulation bodily along the wire core to cover and tightly to embrace the exposed surfaces of the elongated contact element and wire core with continuous insulation.

4. The method of insulating a pin and socket contact assembly including the steps of stripping off the end segment of insulation of an insulated lead wire to expose the wire core, aflixing the exposed wire core to the socket contact, dilating the remainder of the insulation of the lead wire relative to the wire core, moving the dilated insulation bodily along the wire core to cover the socket contact with insulation continuous with the lead wire insulation, and contracting the insulation tightly about the socket contact and wire core.

References Cited in the file of this patent UNITED STATES PATENTS Vickery Mar. 9, 1954 

1. THE METHOD OF INSULATING A CONTACT ASSEMBLY HAVING MATING ELEMENTS INCLUDING THE STEPS OF EXPOSING THE END OF THE WIRE CORE OF AN INSULATED LEAD, AFFIXING THE WIRE END TO THE CONTENT ELEMENT HAVING EXPOSED SURFACES UPON JOINING THE CONTACT ASSEMBLY IN MATING RELATIONSHIPS, LOOSENING THE INSULATION OF THE LEAD RELATIVE TO THE WIRE CORE, AND MOVING THE INSULATION ALONG THE WIRE CORE TO COVER SUBSTANTIALLY 